In the extraction of petroleum products from geologic formations a wide range of properties are encountered. Often the petroleum products, when brought to the surface, are composed of gaseous, liquid and solid components. The gaseous components, known as solution gases, are mainly hydrocarbons with 1 to 4 carbon atoms with smaller amounts of hydrocarbons with 5 or more carbon atoms. According to the well flow rates the gaseous component portion may be uneconomic to collect as collection requires the construction of a gas pipeline, local gas compression and possibly local treatment equipment to remove liquids and particulate contamination.
An example of such a situation is a well drilled to recover heavy oil. Heavy oil is a petroleum product with a higher viscosity compared with normal crude oil. As such its flow rate from the geologic formation to the drilled well is generally less than that of normal crude oil. In the well both the gaseous and liquid components are collected. Sometimes sand or other solid matter is contained in the liquid. The liquid portion containing hydrocarbons and water with suspended solids is raised to the surface by a lifting mechanism and the gaseous portion is vented to the surface, normally via the well casing. This gas is often described as well casing gas.
At most locations a natural gas engine supplies the hydraulic power for the well pump and supplies heat from the engine coolant to prevent freezing of the casing gas. At a typical heavy oil well, with oil production rate of 4 to 80 or more barrels per day (0.6 to 13 m3/d), the oil, water and particulate solids (well output) are collected into a storage tank at the well-head. Due to its relatively high viscosity, it is common practice to heat the stored well output in the storage tank to enhance the separation of the water and solids from the petroleum component. In addition the heating reduces the oil viscosity which allows transfer to a collection tanker. Often the storage tank is vented to the atmosphere so that gases that evolve when the well output is heated escape to the atmosphere. The gas that evolves from the tank is often called tank gas.
At locations where the well casing gas flow is insufficient to power the natural gas engine and/or the tank heater, supplementary fuel, usually pipeline natural gas or locally stored liquid petroleum fuel, for example propane, is used. If there is sufficient well casing gas being evolved from the well, that gas is used for the process heater which maintains the stored oil at the desired elevated temperature and the engine. Excess gas is vented.
Both the vented tank gas and the vented casing gas typically contain 90% or more methane, a potent greenhouse gas with a global warming effect over a 100 year period, per unit of mass, of 21 times that of carbon dioxide, CO2, the reference greenhouse gas. To reduce the greenhouse gas amount from a heavy oil well-head where the gases are vented to atmosphere and to reduce other undesired environmental and health effects from the vented gases, a means of combusting the vented gases is beneficial.
At some sites the heat provided by the engine coolant may be insufficient to prevent freezing of the oil and gas transfer piping in harsh winter conditions.
While an open flare can be used to combust more than 95% of the vented gas, it is generally undesirable for environmental and public relations reasons. There is a need for a system that can provide additional heat to prevent freezing and also combust both the excess well casing gas and the tank gas in an enclosed apparatus to reduce the emissions of methane to the atmosphere and so reduce the greenhouse gas emissions from well sites, and particularly heavy oil well-head sites and to reduce the undesired environmental and health effects from the vented gases.
Casing gas flow measurements from heavy oil well sites show that often the casing gas flow exceeds the gas used by the local engine, if present, and the design capacity of the existing burner. Hence there is a need for a system, method and apparatus that can combust the otherwise vented gases when the vented gas flow rates exceed the capacity of the existing burner and the local engine, if present.
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.